It was half-bird, half-reptile and it soared above the still lagoons of Bavaria 147 million years ago. Researchers have confirmed that Archaeopteryx had a brain and body geared for flight, earning it the moniker of the world's most primitive bird.

Ever since the first fossilized remains were found in 1861, Archaeopteryx has courted controversy. The enigma combines the feathered wings and wishbone of birds with the teeth and long, bony tail characteristic of reptiles, causing many to view it as an intermediate between the two groups. "It became an icon for evolution in action," says Angela Milner, from London's Natural History Museum, who studies the creature.

But some researchers have disputed whether Archaeopteryx ever took to the skies, citing, for example, its lack of a bird-like breastbone as evidence that it lacked the power to take off. Now Milner's team has shown that the animal could fly and was a true, albeit early, bird.

Conker case

The researchers used computed tomography (CT) to peer inside the conker-sized brain-case of the first Archaeopteryx specimen ever to be found. They took over 1,000 X-ray images in various orientations and used them to create a three-dimensional reconstruction of the skull's interior. From this, they were able to infer what the brain was like. Their results are reported in this week's Nature1.

The team believe that Archaeopteryx had enlarged brain regions for vision and movement control, similar to modern-day birds. Its inner ear structure, which helped to control balance, was also bird-like and its brain to body size-ratio resembled that of today's feathered fliers. Such attributes are not found in animals that do not take to the skies.

"This shows that Archaeopteryx was more bird-like than we thought," says Larry Witmer, who studies the evolution of flight at Ohio University College of Osteopathic Medicine. The birds had a keen sense of vision and the movement and balance control needed for coordinated, controlled flight.

Black market

“Archaeopteryx became an icon for evolution in action.”

Angela MilnerPalaeontologist at the Natural History Museum, London

So far, just seven magpie-sized Archaeopteryx specimens have been described. It is rumoured that others have been found, but with rare fossils fetching a high price on the black market, no official details have emerged.

The recognized finds all hail from a 25-square-kilometre patch of quarry in Bavaria, Germany, known as the Solnhofen Limestone. Over a million years ago, the area boasted a series of stagnant lagoons lined with thick silt.

The birds either lived in the area or were passing through when they fell in, speculates Milner. The oxygen-poor waters would have slowed their decay, allowing their feathers and bones to leave intricate impressions in the fine silt.

Half-way house

Although the fossils are a rare and intriguing find, they leave archaeologists yearning for the elusive half-way house between reptiles and birds.

There were flying dinosaurs before and after Archaeopteryx, but their flight surfaces were made from skin, not feathers. "We haven't found any fossils of feathered dinosaurs from before Archaeopteryx," says Witmer, so we have no idea when the first feathered creatures took to the sky.